Strontium isotope analysis in prehistoric cod otoliths by laser ablation multi-collector inductively coupled plasma mass spectrometry

Exploitation of aquatic resources, especially fishing, was a fundamental part of human subsistence during the Late Mesolithic Ertebølle culture (5400–4000/3900 cal BC) in Southern Scandinavia. In this pilot study we examine three cod otoliths from two Late Mesolithic locations in eastern Denmark to see whether local environmental conditions are reflected in the strontium ratios of the fish, to source the fish to either the Atlantic or the Baltic Sea and finally, to explore how fishing was conducted in relation to the settlements. We used laser ablation multi-collector inductively coupled plasma mass spectrometry for sequential sampling of the otoliths for strontium isotope analysis. All three otoliths yielded ⁸⁷Sr/⁸⁶Sr values that fall within the range of Baltic Sea water, thus indicating that cod caught by Mesolithic fishers in the Danish straits belonged to the Baltic Sea stock. Our results suggest that cod were not caught in waters immediately adjacent to the archaeological sites but rather came from the Kattegat. We could not detect any substantial change in habitat between juvenile and mature stages of the fish lives. Our study shows the potential of isotopic analysis to address issues regarding the individual ecological history of fish and human fishing strategies.